In trench type semiconductor devices, such as trench type metal oxide semiconductor field effect transistors (MOSFETs), on-state resistance (RDSon), breakdown voltage and avalanche ruggedness are important performance parameters. The on-state resistance is the drain-to-source resistance of the trench type semiconductor device in an on-state. The breakdown voltage is the voltage at which a reverse biased drift-base p-n junction breaks down and significant current starts to flow between a source and a drain of the trench type semiconductor device by an avalanche multiplication process. In the avalanche multiplication process, impact ionization of electron-hole pairs can generate avalanche current between the drain and a base region of the semiconductor device. The avalanche ruggedness characterizes the trench type semiconductor device's capability to withstand the avalanche current when subjected to, for example, unclamped inductive switching.
Buried electrode or oxide field plate trench type semiconductor devices have been utilized to improve performance parameters, such as higher device breakdown voltage and lower on-resistance. Conventionally, one technique for reducing the on-state resistance in a buried electrode trench type semiconductor device involves reducing the cell pitch of the semiconductor device and consequently shrinking the width of the silicon mesa separating two neighboring gate trenches, in order to increase the doping concentration of a drift region for a desired breakdown voltage. However, reducing the width of the silicon mesa is constrained by the body/source contact formation, which requires a minimum contact opening width for an adequate fill of the contact metallization. In addition, the avalanche ruggedness is of particular concern in applications where the semiconductor device is susceptible to repetitive avalanche cycles, which can lead to significant parametric shift over time if the semiconductor device is not sufficiently rugged.
Accordingly, there is a need to overcome the drawbacks and deficiencies in the art by providing a semiconductor device having a structure to improve avalanche ruggedness and figures of merit, such as on-state resistance and breakdown voltage.